A part of the background hereof lies in the development of light emitters based on direct bandgap semiconductors such as III-V semiconductors. Such devices, including light emitting diodes and laser diodes, are in widespread commercial use.
Another part of the background hereof lies in the development of wide bandgap semiconductors to achieve high minority carrier injection efficiency in a device known as a heterojunction bipolar transistor (HBT). These transistor devices are capable of operation at extremely high speeds. For example, InP HBTs have, in recent years, been demonstrated to exhibit operation at speeds above 500 GHz.
Another part of the background hereof lies in the development of heterojunction bipolar transistors which operate as light-emitting transistors and laser transistors. Reference can be made for example, to U.S. Pat. No. 7,091,082 and to the following: U.S. patent application Ser. No. 10/646,457, filed Aug. 22, 2003; U.S. patent application Ser. No. 10/861,320, filed Jun. 4, 2004; U.S. patent application Ser. No. 11/068,561, filed Feb. 28, 2005; U.S. patent application Ser. No. 11/175,995, filed Jul. 6, 2005; and U.S. patent application Ser. No. 11/364,893, filed Feb. 27, 2006; PCT International Patent Publication Number WO/2005/020287, published Mar. 3, 2005, and PCT International Patent Publication Number WO/2006/006879 published Aug. 9, 2006; all the foregoing being assigned to the same assignee as the present Application. Reference can also be made to the following publications: Light-Emitting Transistor: Light Emission From InGaP/GaAs Heterojunction Bipolar Transistors, M. Feng, N. Holonyak, Jr., and W. Hafez, Appl. Phys. Lett. 84, 151 (2004); Quantum-Well-Base Heterojunction Bipolar Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 1952 (2004); Type-II GaAsSb/InP Heterojunction Bipolar Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., B. Chu-Kung, G. Walter, and R. Chan, Appl. Phys. Lett. 84, 4792 (2004); Laser Operation Of A Heterojunction Bipolar Light-Emitting Transistor, G. Walter, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 85, 4768 (2004); Microwave Operation And Modulation Of A Transistor Laser, R. Chan, M. Feng, N. Holonyak, Jr., and G. Walter, Appl. Phys. Lett. 86, 131114 (2005); Room Temperature Continuous Wave Operation Of A Heterojunction Bipolar Transistor Laser, M. Feng, N. Holonyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 131103 (2005); Visible Spectrum Light-Emitting Transistors, F. Dixon, R. Chan, G. Walter, N. Holonyak, Jr., M. Feng, X. B. Zhang, J. H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 88, 012108 (2006); The Transistor Laser, N. Holonyak, M Feng, Spectrum, IEEE Volume 43, Issue 2, February 2006; Signal Mixing In A Multiple Input Transistor Laser Near Threshold, M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Appl. Phys. Lett. 88, 063509 (2006); and Collector Current Map Of Gain And Stimulated Recombination On The Base Quantum Well Transitions Of A Transistor Laser, R. Chan, N. Holonyak, Jr., A. James, G. Walter, Appl. Phys. Lett. 88, 14508 (2006).
FIG. 1 is a band diagram of a conventional double-heterojunction quantum-well diode laser. Electrons are typically injected from high to low gap (left side of FIG. 1) and holes injected from high gap to low gap (right side of FIG. 1) into a central lower gap quantum well (QW) region where electrons and holes are collected in the QW(s) and recombine generating recombination radiation (photons). The tilted schematic generic mirror arrangement can be, for example, any of an edge-emitter, vertical cavity, or DFB configuration. The heterobarriers of the diode laser serve the further purpose, besides injection, of confining carriers and photons so that the electromagnetic field and stimulated emission can be high (maximum) at the point of recombination, at the QW(s). Besides the parasitic circuit properties of the diode (resistance, capacitance, etc.) the speed of the diode is largely determined by the carrier “pile-up” and how “fast” recombination can reduce (“clean-out”) the stored (injected) charge. Inevitably, at high enough speed, the charge-photon interaction leads to a resonance peak and speed limitation. Charge storage becomes a nuisance. FIG. 2 shows graphs of calculated diode laser charge-photon resonance peaks which pose a limitation to linear frequency response (“speed” of operation). The calculation uses a photon lifetime for a 400 μm cavity length and indicates the effect of recombination lifetime on the charge-photon resonance.
It is among the objects of the present invention to provide two-terminal semiconductor light emitting devices and laser devices which overcome prior art limitations, including those summarized above, and which exhibit improved properties including higher speed of operation. It is also among the objects of the present invention to provide improved methods for producing light emission and laser emission from semiconductor device, including such emission that can be controlled with very fast response time.